This applies to VW pump duse TDI engines, I thought the
group might find this interesting. The 04 to 06 VW tdi's
have been known to wear the lobes off their camshafts,
usually as a result of not using the proper 505.01 spec
engine oil. The first warning sign is usually soot in the
air filter, but no particular driveability symptom. [2006
Volkswagen Jetta TDI, Engine/Propulsion Photo][2006
Volkswagen Jetta TDI, Engine/Propulsion Photo] This could
be picked up at a routine service. As one or more exhaust
lobes on the camshaft begins to wear, lift is reduced, but
the exhaust valve still opens. No noise is present because
the engine has hydraulic lifters (with remarkable ability to
pump up and maintain valve clearance). As the condition
deteriorates, sometimes odd MAF codes are stored,
"implausible signal" etc. Exhaust cannot exit the cylinder
fully because the valve is barely opening, so there is some
reverse flow into the intake the next time the intake valve
opens. It all hits the fan once the top of the lifter gets a
hole worn through it. At that point the lifter collapses and
the exhaust valve doesn't open at all. The four stroke cycle
becomes three- intake, compression, power, and nowhere to
go........ followed by pow! back through the intake plumbing
and intercooler. Here are pics of a worn cam lobe and a
relatively good lobe [2006 Volkswagen Jetta TDI,
Engine/Propulsion Photo][2006 Volkswagen Jetta TDI,
Engine/Propulsion Photo] The car in question actually
drove in with almost 1/4 inch of lift missing from an
exhaust lobe and was backfiring into the intake when given
throttle. If you see significant soot in the air filter, you
may want to suggest inspecting the camshaft before broken
pieces of lifter start floating around.